Heat pipe with capillary structure

ABSTRACT

A heat pipe comprises a first pipe and at least a second pipe. The first pipe includes an evaporator, a heat insulator and a condenser communicating with each other to define a hollow chamber. The second pipe disposed in the hollow chamber includes an accommodating space and a first capillary structure disposed in one end of the accommodating space closer to the evaporator. Two opposite sides of an outer pipe wall of the second pipe directly abut an inner pipe wall of the first pipe. The first pipe further includes a second capillary structure which is disposed in the hollow chamber closer to the evaporator and extended to an outside of the second pipe and occupies at least 2/3 volume of the evaporator. A first part of the first capillary structure and the second capillary structure are connected to each other by winding so as to enhance transportation therebetween.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation In Part (CIP) of an earlier filed,pending, application, having application Ser. No. 14/793,132 and filedon Jul. 7, 2015, the content of which, including drawings, is expresslyincorporated by reference herein.

BACKGROUND OF THE INVENTION Field of Invention

This disclosure relates to a heat pipe and, in particular, to a heatpipe wherein the working fluid is driven by the vapor pressuredifference.

Related Art

A conventional heat pipe is mainly composed of a sealed metal pipe, acapillary structure inside the metal pipe and a heat-transfer fluidfilled in the metal pipe, and besides, a proper vacuum degree is keptinside the metal pipe to lower down the trigger-temperature-differenceof the heat pipe. In the heat pipe, the evaporator of the heat pipe isdisposed at the heat source so that the heat generated by the heatsource can evaporate the fluid (liquid phase) in the pipe into the vapor(vapor phase). The generated vapor is driven by the vapor pressuredifference to flow to the condenser of the heat pipe and then condensesback into the liquid phase after releasing the latent heat, and lastlyis driven by the capillarity to go back to the evaporator through thecapillary structure. Thereby, the heat pipe can transfer the heatrapidly.

Due to its simple structure, high transfer performance and low thermalresistance, the heat pipe has been applied to the electronic field orother heat-dissipation fields for a long time. However, because theelectronic product is continuously enhanced in portability, lightnessand thinness, 4K image, 4G transmission and more adding functions, thegenerated heat thereof is raised increasingly. Therefore, theconventional heat pipe can't meet the requirement of the high heat andhigh heat flux anymore. Accordingly, the heat pipe needs to be furtherenhanced in performance, for example, the manufacturing method of thecapillary structure needs to be improved or the multiple capillarystructures can be used so as to enhance the capillarity of the capillarystructure. However, the above improvements mostly take a longerprocedure and process time and the heat pipe structure formed thereby isalso too complicated. Therefore, the cost and the efficiency of the heatpipe can't be both taken into account.

Furthermore, in the operation of a conventional heat pipe, the vapor andthe working fluid have opposite flowing directions and they are also notinsulated from each other effectively, so that the working fluid needsto overcome the vapor resistance to go back to the evaporator for thenext circulation. Accordingly, the capillary condition of the heat pipeneeds to be strictly satisfied, that is, the interior capillarity needsto be stronger than the resultant force of the vapor pressure, thebackflow resistance of the fluid and the gravity, and then the heat pipecan have the normal circulation.

Therefore, it is an important subject to provide a heat pipe whereby theheat transfer capability can be enhanced under a simple structure designand the requirement of the high heat and high heat flux of theelectronic product can be satisfied.

SUMMARY OF THE INVENTION

In view of the foregoing subject, an objective of the disclosure is toprovide a heat pipe whereby the heat transfer capability can be enhancedunder a simple structure design and the requirement of the high heat andhigh heat flux of the electronic product can be satisfied.

To achieve the above objective, a heat pipe according to the disclosurecomprises a first pipe and at least a second pipe. The first pipeincludes an evaporator, a heat insulator and a condenser whichcommunicate with each other to define a hollow chamber. Two ends of thefirst pipe along an axial direction of the heat pipe are sealed. Thesecond pipe is disposed in the hollow chamber and includes anaccommodating space and a first capillary structure disposed in one endof the accommodating space closer to the evaporator. Two opposite sidesof an outer pipe wall of the second pipe directly abut an inner pipewall of the first pipe. The first pipe further includes a secondcapillary structure which is disposed in the hollow chamber closer tothe evaporator and extended to an outside of the second pipe andoccupies at least ⅔ volume of the evaporator. A first part of the firstcapillary structure and the second capillary structure are connected toeach other by winding so as to enhance transportation therebetween.

In one embodiment, the second pipe is located in a part of theevaporator, a part of the condenser and the whole heat insulator.

In one embodiment, the second pipe is just located in a part of thecondenser and the whole heat insulator.

In one embodiment, a section of the first pipe along a radial directionof the first pipe is a uniform section.

In one embodiment, the first capillary structure is made by metalsintering powder, fiber, mesh or their any combination.

In one embodiment, the second capillary structure is made by metalsintering powder, fiber, mesh or their any combination.

In one embodiment, the second capillary structure contacts a part of theinner pipe wall of the first pipe located at the evaporator and/or apart of the outer pipe wall of the second pipe located at theevaporator.

In one embodiment, the first capillary structure in the second pipe isextended to the outside of the second pipe, and the second capillarystructure outside the second pipe entirely or partially covers the firstcapillary structure extended to the outside of the second pipe.

In one embodiment, the first capillary structure closer to theevaporator is filled in the second pipe.

In one embodiment, the heat pipe further comprises a plurality of secondpipes disposed adjacent to each other in the first pipe.

In one embodiment, the hollow chamber of the first pipe is a channel forvapor, the second pipe is a channel for working fluid. The vapor isdriven by the vapor pressure difference to move in the first pipe andfrom the evaporator to the condenser. The working fluid is driven by thevapor pressure difference to flow in the second pipe and from thecondenser to the evaporator.

In one embodiment, the inner pipe wall and an outer pipe wall of thefirst pipe are made of the same material.

In one embodiment, the second capillary structure is rolled up withmultiple turns in the evaporator.

In one embodiment, the second capillary structure is rolled up withrespect to a traverse direction of the heat pipe in the evaporator.

In one embodiment, the second capillary structure is folded up multipletimes in the evaporator.

In one embodiment, the second capillary structure is stuffed with aninside of the evaporator.

To achieve the above objective, a heat pipe according to the disclosurecomprises a first pipe and at least a second pipe. The first pipeincludes an evaporator, a heat insulator and a condenser whichcommunicate with each other to define a hollow chamber. Two ends of thefirst pipe along an axial direction of the heat pipe are sealed. Thesecond pipe is disposed in the hollow chamber and includes anaccommodating space and a first capillary structure disposed in one endof the accommodating space closer to the evaporator. Two opposite sidesof an outer pipe wall of the second pipe directly abut an inner pipewall of the first pipe. The first capillary structure is extended fromthe second pipe to form a second capillary structure between the innerpipe wall of the first pipe and the second pipe in the evaporator. Thesecond capillary structure occupies at least ⅔ volume of the evaporatorand is folded up multiple times in the evaporator.

In one embodiment, the second capillary structure is stuffed with aninside of the evaporator.

As mentioned above, since the heat pipe of this disclosure includes afirst pipe and a second pipe disposed in the first pipe and a firstcapillary structure is disposed in the portion of the second pipe closerto the evaporator, the vapor can be effectively prevented from flowingback into the second pipe and the working fluid can flow in the secondpipe in a single direction. Since this kind of structure is simple forthe manufacturing, the quality and yield of the heat pipe can beincreased and the cost can be reduced. Furthermore, the heat pipe ofthis disclosure includes the structure of the inner and outer pipes sothat the efficiency of the liquid-vapor circulation in the heat pipe canbe enhanced and the heat transfer capability of the heat pipe can bethus enhanced. Therefore, the heat pipe of this disclosure is especiallysuitable for resisting the temporary heat impact and can effectivelymeet the requirements of high heat and high heat flux.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the detaileddescription and accompanying drawings, which are given for illustrationonly, and thus are not limitative of the present disclosure, andwherein:

FIG. 1A is a schematic diagram of a part of the appearance of the heatpipe of an embodiment of the disclosure;

FIG. 1B is a schematic sectional diagram of the heat pipe of FIG. 1Ataken along the line A-A;

FIG. 1C is a schematic diagram showing the appearance of the heat pipein FIG. 1A which has been flattened;

FIG. 1D is a schematic sectional diagram of the heat pipe in FIG. 1Ctaken along the line B-B;

FIG. 1E is a schematic side sectional diagram of the heat pipe of FIG.1A;

FIG. 1F is a schematic side sectional diagram of the heat pipe ofanother embodiment of the disclosure;

FIGS. 2A to 2C are schematic diagrams of a part of the appearances ofthe heat pipes of other embodiments of the disclosure;

FIG. 3A is a schematic diagram of a part of the appearance of the heatpipe of another embodiment of the disclosure;

FIG. 3B is a schematic diagram of the heat pipe in FIG. 3A under theflattened process;

FIG. 3C is a schematic sectional diagram of the heat pipe in FIG. 3Awhich has been flattened;

FIG. 4A is a schematic diagram of a part of the appearance of the heatpipe of another embodiment of the disclosure; and

FIG. 4B is a schematic sectional diagram of the heat pipe in FIG. 4Ataken along the line C-C.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure will be apparent from the following detaileddescription, which proceeds with reference to the accompanying drawings,wherein the same references relate to the same elements.

FIG. 1A is a schematic diagram of a part of the appearance of the heatpipe of an embodiment of the disclosure, and FIG. 1B is a schematicsectional diagram of the heat pipe of FIG. 1A taken along the line A-A.As shown in FIGS. 1A and 1B, in this embodiment, the heat pipe Hincludes a first pipe 1 and at least a second pipe 2, and a singlesecond pipe 2 is illustrated as an example herein. The first pipe 1includes a hollow chamber 10 and the second pipe 2 is disposed in thehollow chamber 10.

Herein for example, the first pipe 1 is an elliptic cylindricalthin-type hollow pipe, and the section of the first pipe 1 along theradial direction D2 of the first pipe 1 is a uniform section. The pipe 1can be made by, for example, copper, silver, aluminum, their alloy orother metal materials with well heat transfer property. In the practicalapplication, in addition to the second pipe 2, a working fluid (notshown) is also disposed in the pipe 1 and can be any fluid helping theevaporation and heat dissipation, such as inorganic compounds, alcohols,ketones, liquid metal, refrigerant, organic compounds or their anymixture. Moreover, the pipe 1 is not limited here in shape ordimensions, which can be a cylindrical pipe or rectangular pipe and canbe determined according to the surrounding environment, space, heattransfer requirement or temperature.

FIG. 1C is a schematic diagram showing the appearance of the heat pipein FIG. 1A which has been flattened, and FIG. 1D is a schematicsectional diagram of the heat pipe in FIG. 1C taken along the line B-B.As shown in FIGS. 1A, 1C, 1D, in the formation method of the heat pipe Hof this embodiment, the second pipe 2 is disposed in the hollow chamber10 of the first pipe 1, the working fluid is injected into the heat pipeH and then the vacuum process is implemented to the heat pipe H, and thepost-process such as the flattening process is implemented to the firstpipe 1 and the second pipe 2 at the same time. Otherwise, the workingfluid also can be injected after the first pipe 1 and the second pipe 2are made vacuum. In other words, the two ends 11, 12 of the first pipe 1of the heat pipe H of this embodiment along the axial direction D1 areboth sealed.

As shown in FIGS. 1A to 1D, the second pipe 2 of the heat pipe Hincludes an accommodating space 20 and a first capillary structure 21.The first capillary structure 21 is disposed in only a part of theaccommodating space 20. Herein for example, the first capillarystructure 21 is disposed on the side of the accommodating space 20closer to the evaporator E, and favorably, the first capillary structure21 is disposed in the portion of the accommodating space 20 closer tothe end 11 of the heat pipe H for about a third of the length of thesecond pipe 2.

Furthermore, the first capillary structure 21 of this embodiment isformed outside the second pipe 2. Particularly, the first capillarystructure 21 is formed outside the second pipe 2 firstly, and can beformed by the high sintering and/or injection molding, but thisdisclosure is not limited thereto. Besides, before the first capillarystructure 21 is disposed in the second pipe 2, the porosity andpermeability thereof are properly controlled by the forming method so asto increase the amount of the working fluid flowing back to theevaporator, and therefore the capillarity of the capillary structure canbe enhanced and the maximum heat transfer amount (Qmax) of the heat pipecan be effectively increased.

The conventional capillary structure of the heat pipe is made bydisposing a core rod in the metal pipe to fix the metal powder and alsoformed by the high sintering, but the core rod has a high cost and maybe damaged during the process of the sintering or removing the core rod,and even the capillary structure may be also damaged, so that theperformance of the heat pipe is reduced. However, the first capillarystructure 21 of this embodiment is formed on the outside firstly, andthe form of the capillary structure can be designed according to theperformance requirement and won't be limited by the core rod requiredfor the conventional process. Besides, favorably, the quality of thefirst capillary structure 21 can be examined outside the second pipe 2to eliminate the defective products in advance so as to enhance theyield of the heat pipe H.

The formation method of the first capillary structure 21 of thisembodiment is not meant to be construed in a limiting sense. Inpractice, the first capillary structure 21 not only can be made by themetal sintering powder as mentioned above but also can be fiber, mesh ortheir combination. The formation of the first capillary structure 21 canbe determined according to the process or heat-dissipation requirement.

Besides, since the second pipe 2 of the heat pipe H of this embodimentincludes the first capillary structure 21, the vapor can be effectivelyprevented from flowing back into the second pipe 2, and therefore theworking fluid can flow in the second pipe 2 in a single direction.

Two opposite sides 221, 222 of an outer pipe wall 22 of the second pipe2 directly abut an inner pipe wall 14 of the first pipe 1. The innerpipe wall 14 and an outer pipe wall 15 of the first pipe 1 can be madeof the same material.

As shown in FIG. 1E, the structure of the heat pipe H of this embodimentis further illustrated. The first pipe 1 includes an evaporator E, aheat insulator A and a condenser C. The evaporator E, the heat insulatorA and the condenser C communicate with each other to define the hollowchamber 10. The evaporator E and the condenser C are respectively closerto the two ends 11, 12 of the first pipe 1, and the heat insulator A isdisposed between the evaporator E and the condenser C. To be noted,however, the region of the heat insulator A or condenser C is just forthe illustrative purpose and not meant to be construed in a limitingsense. In this embodiment, the second pipe 2 is located in a part of theevaporator E, a part of the condenser C and the whole heat insulator A.However, this disclosure is not limited thereto. In other embodiments(such as FIG. 1F), the second pipe 2 a of the heat pipe H1 is justlocated in a part of the condenser C and the whole heat insulator A.

In the application of the heat pipe H, one end of the heat pipe Hdisposed at the heat source is the evaporator E of the heat pipe H, andanother end of the heat pipe H disposed away from the heat source is thecondenser C of the heat pipe H. During the heat dissipation, the workingfluid closer to the evaporator E will be evaporated into vapor due tothe latent heat generated by the heat source, and the evaporated workingfluid will flow towards the condenser C of the first pipe and willcondense into the liquid working fluid during the process of moving tothe condenser C. At this time, the evaporator E is a high pressureregion due to the evaporation while the condenser C is a low pressureregion due to the condensation. Accordingly, the vapor pressure formedin the heat pipe H will drive the vapor to move within the firs pipe 1and from the evaporator E, through the heat insulator A and to thecondenser C and drive the working fluid to move within the second pipe 2and from the condenser C, through the heat insulator A and to theevaporator E. That is, the condensed working fluid can be pushed intothe second pipe 2 by the vapor pressure and be transferred within thesecond pipe 2 and to the evaporator E. In other words, the heatgenerated by the heat source can evaporate the working fluid (liquidphase) within the pipe into the vapor (vapor phase). The generated vaporis driven by the vapor pressure difference to flow to the condenser C ofthe heat pipe H and then condenses back into the liquid working fluidafter releasing the latent heat. Accordingly, the continuous circulationwill provide the heat pipe H with the heat-dissipation effect.

Accordingly, the heat pipe H of this embodiment can enhance the heattransfer capability by improving the liquid-vapor circulation. Besides,since the backflow of the working fluid is driven by the vapor pressure,the heat pipe H will undergo less problem of resisting the gravity andcan sustain the abrupt increase of the heat source power. Favorably,since the heat pipe H of this embodiment is simple in structure, thequality and yield of the heat pipe can be increased and the cost can bereduced.

FIGS. 2A and 2B are schematic diagrams of a part of the appearance ofthe heat pipes of other embodiments of the disclosure. To be noted, thestructures of the heat pipes H2, H3 are substantially similar to theheat pipe H1 of the above embodiment, but the heat pipes H2, H3 includesecond capillary structures 13 b, 13 c which are disposed in the hollowchamber 10 b, 10 c closer to the end 11 of the heat pipes H2, H3. Inother words, the first capillary structures 21 b, 21 c and the secondcapillary structures 13 b, 13 c are all disposed closer to the end 11 ofthe heat pipes H2, H3. The second capillary structure 13 b of the heatpipe H2 is fiber or favorably mesh, and the second capillary structure13 c of the heat pipe H3 is fine fiber.

As shown in FIG. 2A, in the heat pipe H2 of this embodiment, the secondcapillary structure 13 b contacts a part of the inner pipe wall 14 b ofthe first pipe 1 b located at the evaporator E and/or a part of theouter pipe wall 24 b of the second pipe 2 b located at the evaporator E.The first capillary structure 21 b of in the second pipe 2 b can beextended to the outside of the second pipe 2 b. At least a part of thefirst capillary structure 21 b and the second capillary structure 13 bextended to the outside of the second pipe 2 b connect to each other oroverlap each other, so as to transfer the fluid in the second pipe 2 bto the outside of the second pipe 2 b and also prevent the vapor fromflowing back into the second pipe 2 b.

In practice, the relation between the first capillary structure andsecond capillary structure is not limited to the above-mention case. Forexample, at least a part of the first capillary structure 21 c of theheat pipe H3 and the second capillary structure 13 c extended to theoutside of the second pipe 2 c connect to each other by winding so as toachieve a better effect on the transportation therebetween.

As shown in FIG. 2C, the first capillary structure 21 d of the heat pipeH4 is extended to the outside of the second pipe 2 d to form the secondcapillary structure 13 d disposed between the inner pipe wall 14 d ofthe first pipe 1 d and the outer pipe wall 24 d of the second pipe 2 d.In other words, in this embodiment, the first capillary structure 21 dextended to the outside of the second pipe 2 d is also the secondcapillary structure 13 d of the heat pipe H4, and therefore the processcan be simplified.

To be noted, the formation methods of the first capillary structures 21b, 21 c, 21 d and second capillary structures 13 b, 13 c, 13 d in theheat pipes H3, H4, H5 are not meant to be construed in a limiting sense,and they can be made by metal sintering powder, fiber, mesh or their anycombination. Besides, the first capillary structures 21 b, 21 c, 21 dand the second capillary structures 13 b, 13 c, 13 d can be madedifferent or the same.

In FIGS. 2B and 2C, the second capillary structure 13 c, 13 d isdisposed in the hollow chamber closer to the evaporator E1 and extendedto an outside of the second pipe 2 c, 2 d. The second capillarystructure 13 c, 13 d is between the end 11 c, 11 d and the second pipe 2c, 2 d. The second capillary structure 13 c, 13 d occupies at least ⅔volume of the evaporator E1 and is stuffed with an inside of theevaporator E1.

Like FIG. 1D, the two opposite sides of the outer pipe wall of thesecond pipe 2 c, 2 d may directly abut the inner pipe wall of the firstpipe 1 c, 1 d. The inner pipe wall and the outer pipe wall of the firstpipe 1 c, 1 d can be made of the same material.

In FIG. 2B, the first part 211 c of the first capillary structure 21 cand the second capillary structure 13 c are connected to each other bywinding so as to enhance transportation therebetween. The secondcapillary structure 13 c is rolled up with multiple turns in theevaporator E1. The second capillary structure 13 c is rolled up withrespect to a traverse direction D of the heat pipe H3 in the evaporatorE1. For example, the second capillary structure 13 c may have anuninterrupted section which is rolled up with multiple turns withrespect to a traverse direction D of the heat pipe H3 in the evaporatorE1. The outermost turn 131 c of the second capillary structure 13 cdiscretely contacts the inner pipe wall 14 c of the first pipe 1.

In FIG. 2C, the first capillary structure 21 d is extended from thesecond pipe 2 d to form a second capillary structure 13 d between theinner pipe wall 14 d of the first pipe 1 d and the second pipe 2 d inthe evaporator E1. The second capillary structure 13 d occupies at least⅔ volume of the evaporator E1 and is folded up multiple times in theevaporator E1. For example, the second capillary structure 13 d may havean uninterrupted section which is folded up multiple times at its folds132 d-134 d. An acute angle at the fold is formed by folding up. A totalheight of the folded second capillary structure 13 d can make theoutermost surface 135 d of the folded second capillary structure 13 dfirmly contact the inner pipe wall 14 d of the first pipe 1 d.

FIG. 3A is a schematic diagram of a part of the appearance of the heatpipe of another embodiment of the disclosure, FIG. 3B is a schematicdiagram of the heat pipe in FIG. 3A under the flattened process, andFIG. 3C is a schematic sectional diagram of the heat pipe in FIG. 3Awhich has been flattened. In this embodiment, the structure of the heatpipe H5 is substantially similar to the heat pipe H2 of the aboveembodiment, but the inner pipe wall 14 e of the first pipe 1 e at thetwo ends 11 e, 12 e contacts the outer pipe wall 24 e of the second pipe2 e after the flattened process. When the heat pipe H5 is flattened, thesecond capillary structure 13 e outside the second pipe 2 e can entirelyor partially cover the first capillary structure 21 e extended to theoutside of the second pipe 2 e, so as to effectively enhance the heattransfer efficiency of the heat pipe H5.

FIG. 4A is a schematic diagram of a part of the appearance of the heatpipe of another embodiment of the disclosure, and FIG. 4B is a schematicsectional diagram of the heat pipe in FIG. 4A taken along the line C-C.As shown in FIGS. 4A and 4B, in comparison with the above embodiments,the heat pipe H6 includes a larger first pipe 1 f. In other words, thefirst pipe 1 f includes a larger hollow chamber 10 f. The heat pipe H6includes a plurality of second pipes 2 f which are disposed adjacent toeach other in the first pipe 1 f. Through the disposition of the pluralsecond pipes 2 f, the flat heat pipe H6 can be made with a greater area.Since the heat pipe H6 of this embodiment also undergoes the flattenedprocess, the inner surface of the first pipe 1 f presses the outer pipewall of the second pipe 2 f, and therefore the second pipe 2 f can serveas the support structure of the heat pipe H6 to prevent the depressionand deformation of the heat pipe H6.

Summarily, since the heat pipe of this disclosure includes a first pipeand a second pipe disposed in the first pipe and a first capillarystructure is disposed in the portion of the second pipe closer to theevaporator, the vapor can be effectively prevented from flowing backinto the second pipe and the working fluid can flow in the second pipein a single direction. Since this kind of structure is simple for themanufacturing, the quality and yield of the heat pipe can be increasedand the cost can be reduced. Furthermore, the heat pipe of thisdisclosure includes the structure of the inner and outer pipes so thatthe efficiency of the liquid-vapor circulation in the heat pipe can beenhanced and the heat transfer capability of the heat pipe can be thusenhanced. Therefore, the heat pipe of this disclosure is especiallysuitable for resisting the temporary heat impact and can effectivelymeet the requirements of high heat and high heat flux.

Although the disclosure has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternative embodiments, will be apparent to persons skilled in the art.It is, therefore, contemplated that the appended claims will cover allmodifications that fall within the true scope of the disclosure.

What is claimed is:
 1. A heat pipe, comprising: a first pipe includingan evaporator, a heat insulator and a condenser which communicate witheach other to define a hollow chamber, wherein two ends of the firstpipe along an axial direction of the heat pipe are sealed; and at leasta second pipe disposed in the hollow chamber and including anaccommodating space and a first capillary structure disposed in one endof the accommodating space closer to the evaporator; wherein twoopposite sides of an outer pipe wall of the second pipe directly abut aninner pipe wall of the first pipe, the first pipe further includes asecond capillary structure which is disposed in the hollow chambercloser to the evaporator and extended to an outside of the second pipeand occupies at least ⅔ volume of the evaporator, a first part of thefirst capillary structure and the second capillary structure areconnected to each other by winding so as to enhance transportationtherebetween.
 2. The heat pipe as recited in claim 1, wherein the secondpipe is located in a part of the evaporator, a part of the condenser andthe whole heat insulator.
 3. The heat pipe as recited in claim 1,wherein the second pipe is just located in a part of the condenser andthe whole heat insulator.
 4. The heat pipe as recited in claim 1,wherein a section of the first pipe along a radial direction of thefirst pipe is a uniform section.
 5. The heat pipe as recited in claim 1,wherein the second capillary structure contacts a part of the inner pipewall of the first pipe located at the evaporator and/or a part of theouter pipe wall of the second pipe located at the evaporator.
 6. Theheat pipe as recited in claim 1, wherein the first capillary structurein the second pipe is extended to the outside of the second pipe, andwhen the heat pipe is flattened, the second capillary structure outsidethe second pipe entirely or partially covers the first capillarystructure extended to the outside of the second pipe.
 7. The heat pipeas recited in claim 1, wherein the first capillary structure closer tothe evaporator is filled in the second pipe.
 8. The heat pipe as recitedin claim 1, further comprising: a plurality of second pipes disposedadjacent to each other in the first pipe.
 9. The heat pipe as recited inclaim 1, wherein the hollow chamber of the first pipe is a channel forvapor, the second pipe is a channel for working fluid, the vapor isdriven by the vapor pressure difference to move in the first pipe andfrom the evaporator to the condenser, and the working fluid is driven bythe vapor pressure difference to flow in the second pipe and from thecondenser to the evaporator.
 10. The heat pipe as recited in claim 1,wherein the inner pipe wall and an outer pipe wall of the first pipe aremade of the same material.
 11. The heat pipe as recited in claim 1,wherein the second capillary structure is rolled up with multiple turnsin the evaporator.
 12. The heat pipe as recited in claim 1, wherein thesecond capillary structure is rolled up with respect to a traversedirection of the heat pipe in the evaporator.
 13. The heat pipe asrecited in claim 1, wherein the second capillary structure is folded upmultiple times in the evaporator.
 14. The heat pipe as recited in claim1, wherein the second capillary structure is stuffed with an inside ofthe evaporator.
 15. A heat pipe, comprising: a first pipe including anevaporator, a heat insulator and a condenser which communicate with eachother to define a hollow chamber, wherein two ends of the first pipealong an axial direction of the heat pipe are sealed; and at least asecond pipe disposed in the hollow chamber and including anaccommodating space and a first capillary structure disposed in one endof the accommodating space closer to the evaporator; wherein twoopposite sides of an outer pipe wall of the second pipe directly abut aninner pipe wall of the first pipe, the first capillary structure isextended from the second pipe to form a second capillary structurebetween the inner pipe wall of the first pipe and the second pipe in theevaporator, the second capillary structure occupies at least ⅔ volume ofthe evaporator and is folded up multiple times in the evaporator. 16.The heat pipe as recited in claim 15, wherein the second capillarystructure is stuffed with an inside of the evaporator.